Voltage Source HVDC Overview Mike Barnes Tony Beddard Note: This is a version with images removed which have copyrighted other than from the University of Manchester, for web publication. Should a conference attendees want a fuller version, please contact mike.barnes@manchester.ac.uk
Contents 1. Background LCC and VSC 2. Multi terminal terminal 3. Circuit Breakers 4. Cable Modelling 5. Availability 6. Concluding comments
AC vs DC Issue AC DC Vlt Voltage conversion Transformers Power electronics Protection Transmission distance Current and voltage fall to zero twice per cycle Limited by reactive power consumption Breakers complex No Reactive power requirement (on DC side) System cost Cheap terminal cost Expensive terminal Line or cable more Cheaper line or cable cost expensive per mile per mile Space requirement Lower terminal footprint Greater terminal footprint Greater line footprint Lower line footprint Interconnected systems Must have same frequency Asynchronous connection and phase In early 20 th Century technology available meant AC was preferred for transmission
Revival of DC High Voltage Transmission Initially Current Source (thyristor based) Large station footprint Strong AC system needed
Operation: Thyristorcontrol delays current flow with respect to input voltage Phase shift controls real power flow (P) Phase shift draws large amounts of reactive power (Q)
Current Source (CS) or Line Commutated Converter (LCC) Examples Yunnan Guangdong (2009) 5000MW, +/ 800kV Bipolar 1418km Three Gorges (2004) 3000MW, +/ 500kV Bipolar 940km Melo (2011) 500MW, Back to Back
However: Need to connect vast amounts of offshore wind Need to interconnect more networks, even those unsynchronised Issues with CS HVDC: Station footprint Need for strong AC network to connect to Needs to use mass impregnated oil cable
New Power Generation / New Solution Voltage Source (VS) HVDC Main advantages of VSC over CS: Smaller footprint t( (offshore platform ltf cheaper) Power direction in cable changed by current (keep same polarityv V, use cheaper XLPEcable) No need for reactive power generation to supply converter
Evolution of VSC HVDC Technology Year first Losses per scheme converter Technology commissioned Converter Type (%) Switching frequency (Hz) Example Project HVDC Light 1st Gen 1997 Two Level 3 1950 Gotland HVDC Light 2nd 2000 Three level Diode NPC 2.2 1500 Eagle Pass Gen 2002 Three level Active NPC 1.8 1350 Murraylink HVDC Light 3rd Two Level with Gen 2006 OPWM 1.4 1150 Estlink Trans Bay HVDC Plus 2010 MMC 1 <150* Cable HVDC MaxSine 2014IP MMC 1 <150* SuperStation HVDC Light 4th Gen 2015IP CTL 1 =>150* Dolwin 2 *switching frequency is for a single module/cell.
CS vs VSC HVDC Current Source HVDC Available since 1950 s Loss 0.8% per converter station Voltage Source Converter HVDC Loss 1.1% per converter station Much smaller footprint Newer technology (since 1997) ZDF
First Offshore Installation Troll 1&2 88MW (2005), 3&4 100MW (2015) +/ 60kV DC, 70km 132kV AC on shore to 56kV or 66kV offshore
First Offshore Windfarm: BorWin1 2009 First wind farm installation: BorWin1=80x5MW turbines ABB 2 level lconverter Only existing offshore VSC HVDC windfarm connection
BorWin1 Design Design for maximising availability and minimising maintenance: DC choppers onshore No tap changing transformer offshore Planned in service date 2009/10.
First Multi Level Converter Trans Bay Cable 2010 First MMC Multilevel system
Issues Many, but key issues include: Multi terminal control Breakers Availability Cable Modelling
2. Multi Terminal Control How to control? Levels / hierarchy / software algorithms Hardware to facilitate control
Prior Art Shin Shinano 50MVAx3 back to back GTO VSC HVDC SACOI CS HVDC 3 terminal link 200MW/50MW/200MW Hydro Quebec CS HVDC Planned at 5 terminal, installed as 3 Most usually run effectively as point to point
Present proposed control Local droop line control at each station Local droop line control at each station Super imposed master slave central control (telecommunications)
However No operational experience with ihvs HVDC multi terminal systems which are: large scale not co located Planned systems: Tres Amigas Texas Scotland Shetland Offshore North thsea in Europe Atlantic Offshore Wind Connection
Circuit Breakers How to manage DC fault? No DC circuit breakers Faults cleared on AC side (at present)
3. Breakers Available Limited Passive Resonance Breaker Test designs constructed Relatively low interruption speed Based on Metallic Return Transfer Breaker in CS HVDC Full Current, Limited Voltage
Preferred topologies HVDC Breaker Review Hybrid Circuit Breaker Low on state losses Relatively slow interruption speed Solid state Circuit Breaker High on state losses Fast Interruption speed
ABB Patent Medium Voltage Prototype Built
4. HVDC Cable Modelling No standard model What models are commercially available? Differences between the models Background theory Implementation ti
HVDC Cable Models Pi Section Lumps cable s RLC parameters Adequate for steady state simulations with short lengths of cable Computational intensive if many pi sections are required Bergeron Model Represents distributed nature of LC with R lumped Does not account for frequency dependent nature of parameters Frequency dependent models Distributed RLC model frequency dependency of all parameters Mode model does not account for frequency dependent transformation matrix. Phase model said to be the most robust and numerically accurate cable model commercially available
5. VSC HVDC Availability Analysis Typical Radial Scheme for an UKRound 3 Windfarm: Determine overall availability of scheme Identify key components which effect the scheme Availability statistics are next to non existent Radial VSC HVDC Scheme
Results Overall energy availability of 96.5% Component Importance for Availability DC Cable Offshore Reactor Other Offshore Equipment Offshore MMC Offshore DC Switchyard Onshore Equipment 8% 9% 9% 10% 10% 54%
6. In Conclusion Absence of history, data and experience with voltage source HVDC Offshore/ MMC No defined standards Hardware or Control Intra operability issue (for multi manufacturer systems) Developing technology Unavailability: cables, instrumentation and software, transformers Reliability: Big question is how to manage multi terminal
References Siemens The Smart Way: HVDC Plus One step ahead, Company Brochure, Siemens AG, 2009. (online) Jacobson B, Jiang Häfner, Y, Rey, P, Asplund, G, Jeroense, M, Gustafsson, A and Bergkvist, M HVDC with Voltage Source Converters and Extruded Cables up to +/ 300kV and 1000MW, CIGRE. 2006 (online, ABB website) ABB HVDC and HVDC Light, accessed September 2010. http://www.abb.com/hvdc. p// / National Grid, Offshore Information Development Statement (ODIS), Sept 2010 and 2011, online Rui et al,, Multi terminal HVDC Grid a Case Study of a possible Offshore Grid in the Norwegian Sea, PowerTech 2011, paper 181 Greiner et al, Availability Evaluation of Multi Terminal DC Networks with DC Circuit Breakers, PowerTech 2011, paper 451 Dodds, S et al, HVDC VSC transmission operating experiences, Cigre 2010, paper B4_203_2010 Vancers, I et al, A Survey of the Reliability of HVDC Systems Throughout the world During 2005 6, Cigre 2009, Paper B4 119